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122 Gas Turbine Handbook: Principles and Practices
get differential pressure is reached. Manual activation of the cleaning
mechanism should be considered only after the unit has reached its
target differential pressure and the interval between cleaning cycles
becomes noticeably short.
Other factors such as velocity of the air through the filter, the
filter media’s ability to tolerate moisture, and air leaks around the
doors and windows also influence filter performance. Deteriorated
seals around the filter elements and air leaks around the doors are
especially detrimental to the effectiveness of inertial separator type
filters (as they reduce the velocity through the separator).
FILTER & GAS TURBINE MATCH
The filter selection should be matched to the site environment,
the gas turbine type, and economics. This selection should be based
on the contaminants at the site location, the air flow into and through
the gas turbine, and the level of support located on site. For example,
a self-clean cannister type filter system may be well suited for the
desert environment where sand storms will load it up quickly, and
the self-clean feature will maintain its efficiency and pressure drop
at an acceptable level. However, it is ill suited for installations where
the element takes too long to load up, and where it does not filter a
majority of the contaminants that are detrimental to the gas turbine.
Figure 8-4 provides a comparison of the effectiveness of various filter
types.
INLET AIR COOLING
Rating Curve
Gas turbines are rated for a power output level ( horsepower or
megawatts) at a temperature and altitude condition. Two standards
used are the International Standards Organization (ISO) and the
National Electrical Manufacturers Association (NEMA). ISO conditions
are defined as 59°F inlet temperature, 14.7 psia inlet pressure,
and 60% relative humidity, and NEMA conditions are defined as 80°F
inlet temperature and 1,000-foot elevation. For surface applications, a
rating curve showing power vs. inlet temperature is widely used (Fig-